Electroplated chromium aritcle



latented @em 279 1932 rr o ELECTRXDMTED CHEEMUM all.lill@Gld@A i r i a. metal having a passive surface, or surtace iilin of impurities. vrllhe surface film mediately, in some cases.

impedes the adherence ot el-ectrodeposited metal to the hase metal and prevents intimate union'o'l the metallic coating with the ravv metal beneath the film.

Surface films come on metals due to oxidination, sulphurization, or other forms of tarnishing or corrosion. Practically all metalsa to some extent, taire on such surface films, hut the rapidity of 'formation varies with the dilerent metals. Some metals produce sur'- ace lnis relatively slowly, While other metals "form such ilms rapidly,-almost iniln a metal oi7 the former class, the coating can he applied directly to the surface. ln the present pracf tisej the metal is first thoroughly cleaned and all foreign matter removed trom the surface.v

rl`he cleaned metal is then dipped in the plating hath and the plating or coating applied. The surface of the metal remains clean long enough to enable the coating to he applied and the coating metal to adhere to the raw, hase metal.` ln a metal of the latter class, the surface lilm forms so quickly that it is impossible to apply the coating henore formation et the The ordinary process for electroplatingl does not, therefore, vvorlr Well with metal of this class, as the coating does not adhere firmly due to the presence of the Uur present invention produces a process hy which a metallic coating is made to adhere to the surface ci a metal having a. passive surface or a surtace iilm. ln its fundamental aspect, the invention resides in the use of an acid plating hath, in contradistnction to alkaline loaths such yas have been hitherto universally employed. ln addition he invention is intended to produce anv Application illecl February le, 3.9529. Serial No. Seduta.

to supplying the ions for the metallic coating, the acid bath eats into the surface of the hase metal suliciently to remove the surface hlm and expose the ravi metal beneath? to which the .metallic coating adheres firmly.

ln other Words, the surface is removed hy the. acid bath simultaneously with the deposition ot the metallic coatinge ln the preferred embodiment the invention, the plating hath is strongly acid and contains a small amount of metal in solution for decomposition in the process and tor supplying the coitingL` characteristics mentioned :tor short time so that a thin layer of the coated meta-l is formed thereon and the acid does not act lo enough to impair themetal. Alter this tl coatfng has been applied, the metal is opiich rinsed and washed so as to remove all tracesv ot acid. rlhe coating metal selected is such thatit can, in turni he plated in the usual manner, hy the use of alkaline baths9 further coatings may loe huilt up on it, until the finishing layer is obtained.'

rl`he inventionvvill novv he 'urt ier' illustrated with chromium taken hy vvay of en- The nietalto'he plated or coated is dipped in the hath having1 the With failure loecause the passive surface or.

surface film 'of the chromium made it dimcult to cause the electrodeposited coating to adhere thereto. @ur present invention overcomes this diculty and the plating is caused to adhere hy striking the'chromium with a metal, preferably copper, in anacid solution, preferably strong hydrochloric acid (C. P. HC1) containing a very small amount of copper chloride. lln this Way, a very thin layer of copper is firmly axed to the chromlum surface and on this layer further metallic layers can be built up in the customary manner without difliculty.

The copper strike or bath may be made up as follows Twenty cubic centimeters 2O c. c.) of a stock copper chloride solution, one gram of copper metal to the .twenty cubic centimeters) are added to a four. (4) liter beaker nearly full of hydrochloric acid, C. P. HC1. Commercial hydrochloric acid will not work so well. No water is added. The solution thus obtained is employed as the copper strike bath. The solution provides a strong acid plating bath with a small amount of metallic or copper ions for decomposition therefrom and deposition on the chromium as a coating.

Preferably, two sheet copper anodes (each 1%XS) are used with the above copper strike. p

The current is preferably connected before hand and the chromium is allowed to remain in the bath OrfStrike for about three seconds with full current flowing at around 9 or i' 10 Volts. A thin bright deposit of copper is then obtained on the chromium.

The chromium is now removed, is washed and rinsed quickly and is promptly passed into a warm copper cyanide bath. It is prefto remain in the cyanide bath for about 4 seconds with full current flowing at around 9 or 10 volts. The cyanide bath gives a thicker copper coating to the surface and in this way the chromium is copper plated. The cyanide bath may be usual or stock composition.

II' silver plating is desired, the same can be built up on the copper layers. The silver is also preferably applied in coatings or layers, the rst of which is rather thin and the second thick. The first is preferably obtained by a silver cyanide strike, with full current owing at around 9 or 10 volts and for about seconds. The silver strike may be a solution which contains .18 to .23 ounces of silver per gallon and 9 to 10 ounces of potassium cyanide per gallon. This composition is to be taken merely b way of example. The silver strike provi es a thin silver deposit on top of the copper and to this thin silverlayer the selected to providethe initial thin coating should be such that other metallic coatings can be made to adhere thereto by the usual alkaline baths so that a coating suiciently thick may be vbuilt up.

What is claimed is:

An electroplated product comprising a base of chromium, a coating of copper firmly ad.v

hering to the chromium, and a coating of silver firmly adhering to the copper coating. In testimony whereof, we have hereunto set our hands.

DANIEL GRAY.

BURDETTE K. NORTHROP. A.

loo

full silver deposit can be applied and will adhere firmly.

The use of the acid strike or bath makes it possible to plate the chromium. The acid eliminates the passive surface condition o r surface lm of the chromium, and the solution rovides the copper or other metallic ions whic come into direct contact with the raw chromium metal beneath the surface, adhere firmly thereto and Vprovide the coating. The

solution selected by way of example is a copper acid solution, for copper is a metal in oo mmon use in electroplating. Other metals be used as well.' lIn general, the metal iis 

